This invention relates generally to a warning sound generator such as the horn of an automobile, and particularly to a generator that uses an IC to produce a euphonious sound.
With automobile horns it is particularly desirable that the sound include two tones of different basic frequency components rather than be a sound of one clear tone. The two tones in this case have basic frequency components in the 200-700 Hz range. The sound pressure component of the sound that is produced should comprise a higher order harmonic tone within the frequency range of 1-3 KHz, which is most suitable for producing a pleasant sound.
In automobile horns a piezoelectric element is used to drive a diaphragm to produce the sound. An example of this kind of sound generator is shown in Japanese Patent Disclosure (KOKAI) No. 57-210395. Two oscillator circuits are provided for producing two pulse signals having different basic frequency components for producing a chord. These two pulse signals are modulated under different conditions so that they each include the above basic frequency components as well as many special higher order harmonics. These pulse-train signals drive the piezoelectric element to produce a warning sound comprising a chord.
However with a device constructed as described above, two separate oscillator circuits and two modulator circuits must be used, resulting in a complicated device. It is also not possible to freely set the higher harmonic components, which is a major requirement in determining the timbre of the sound that is produced, so that it is difficult to produce a horn that has a pleasant sound.
In order to solve this problem, a microcomputer may be used to form a signal having a waveform synthesized from two different basic frequency components for driving the horn, which is a technology that is known from electronic musical instruments and synthesizers, for example. However, using a microcomputer for the horn of an automobile is silly, and prohibitively expensive.
This problem has been solved through the use of a melody generation IC which has a memory function for storing waveform data or a very low-power, low-cost microcomputer such as a 1-bit microprocessor, thereby eliminating the need for a microcomputer that can perform such complicated calculations. By using a piezoelectric element in the horn it is possible to produce a sound of any particular timbre by continuously outputting a square wave pulse. Accordingly, two types of square wave pulses for generating a predetermined sound are stored in two separate memories and the sound is generated based on the waveform signal read out from these memories.
This kind of structure, however, has the drawback that at least two memories, two integrated circuits or a microcomputer are required, which makes it difficult to simplify the structure.